Electric butterfly valve, also known as concrete precast hollow slab inflatable core mold, bridge inflatable core membrane, internal mold. It is mainly used for the pouring and forming of highway bridge concrete pre tensioned and post tensioned beams. It is also used in culvert drainage works. The electric butterfly valve is an expandable and contractible internal mold with different shapes (a product made by vulcanizing with the fiber reinforcement layer, which has high compressive strength, elasticity and air tightness), which is vulcanized from the polymer and high-strength fiber cloth. After being filled with compressed air, the expansion reaches the design requirements of its section. The inflation pressure is determined according to the manufacturer's logo. The capsule can also be extracted from the cavity. It is easy to use, economical and durable. It is soft and shrinks when not inflated, and can be folded and curled at will. After inflated and expanded, it has sufficient strength to withstand the pressure of concrete. It can replace the original wood mold, bamboo mold and steel mold, and can be reused for many times. It is a supporting product of concrete products that can reduce costs and speed up construction progress.